2 research outputs found
Dissolution Kinetics of Hot Compressed Oxide Glasses
The
chemical durability of oxide glasses is an important property
for a wide range of applications and can in some cases be tuned through
composition optimization. However, these possibilities are relatively
limited because around 3/5 of the atoms in most oxide glasses are
oxygens. An alternative approach involves post-treatment of the glass.
In this work, we focus on the effect of hot compression on dissolution
kinetics because it is known to improve, for example, elastic moduli
and hardness, whereas its effect on chemical durability is poorly
understood. Specifically, we study the bulk glass dissolution rate
of phosphate, silicophosphate, borophosphate, borosilicate, and aluminoborosilicate
glasses, which have been compressed at 0.5, 1.0, and 2.0 GPa at the
glass transition temperature (<i>T</i><sub>g</sub>). We
perform weight loss and supplementary modifier leaching measurements
of bulk samples immersed in acid (pH 2) and neutral (pH 7) solutions.
Compression generally improves the chemical durability as measured
from weight loss, but the effect is highly composition- and pressure-dependent.
As such, we show that the dissolution mechanisms depend on the topological
changes induced by permanent densification, which in turn are a function
of the changes in the number of nonbridging oxygens and the network
cross-linking. We also demonstrate a direct relationship between the
chemical durability and the number of chemical topological constraints
per atom (<i>n</i><sub>c</sub>) acting within the molecular
network
Pressure-Induced Changes in Interdiffusivity and Compressive Stress in Chemically Strengthened Glass
Glass exhibits a significant change
in properties when subjected
to high pressure because the short- and intermediate-range atomic
structures of glass are tunable through compression. Understanding
the link between the atomic structure and macroscopic properties of
glass under high pressure is an important scientific problem because
the glass structures obtained via quenching from elevated pressure
may give rise to properties unattainable under standard ambient pressure
conditions. In particular, the chemical strengthening of glass through
K<sup>+</sup>-for-Na<sup>+</sup> ion exchange is currently receiving
significant interest due to the increasing demand for stronger and
more damage-resistant glass. However, the interplay among isostatic
compression, pressure-induced changes in alkali diffusivity, compressive
stress generated through ion exchange, and the resulting mechanical
properties are poorly understood. In this work, we employ a specially
designed gas pressure chamber to compress bulk glass samples isostatically
up to 1 GPa at elevated temperature before or after the ion exchange
treatment of a commercial sodiumāmagnesium aluminosilicate
glass. Compression of the samples prior to ion exchange leads to a
decreased Na<sup>+</sup>āK<sup>+</sup> interdiffusivity, increased
compressive stress, and slightly increased hardness. Compression after
the ion exchange treatment changes the shape of the potassiumāsodium
diffusion profiles and significantly increases glass hardness. We
discuss these results in terms of the underlying structural changes
in network-modifier environments and overall network densification